This invention relates to novel compositions of the formula Cu3Ta3MO12 wherein M is Al, Ga, Fe, Cr, Sc or mixtures thereof.
The use of dielectric materials to increase capacitance is well known and long-used. Earlier capacitor dielectrics fell into two categories. The first category of dielectrics has a relatively temperature-independent dielectric constant but the value of the dielectric constant is low, e.g., 5-10. Materials such as electrical porcelain and mica fall in this category. The second category of dielectrics has very high dielectric constant, e.g., 1000 or more, but they are quite frequency dependent. An example is barium titanate, BaTiO3.
Since the capacitance is proportional to the dielectric constant, high dielectric constant materials are desired. In order to perform acceptably in electronic circuits the dielectric must have a dielectric constant that exhibits minimal frequency dependence. It is also desirable to have the loss or dissipation factor as small as possible.
This invention provides compositions of the formula Cu3Ta3MO12 wherein M is Al, Ga, Fe, Cr, Sc or mixtures thereof. These compositions are useful, for example, in electronic devices as they have high dielectric constant and low loss over a frequency range of from 1 kHz to 1 MHz. They are especially useful as capacitors in electronic devices such as phase shifters, matching networks, oscillators, filters, resonators, and antennas comprising interdigital and trilayer capacitors, coplanar waveguides and microstrips. Also provided is the use of the composition in a process of making a capacitor.
The compositions of this invention are Cu3Ta3MO12 wherein M is Al, Ga, Fe, Cr, Sc or mixtures thereof. These compositions are useful, for example, in electronic devices as they have dielectric properties that provide advantages in such devices requiring a high dielectric constant with minimal frequency dependence and low loss. These compositions have particular use as a capacitor.
The compositions of this invention can be synthesized by the following procedure. Stoichiometric amounts of the starting materials are thoroughly mixed. The starting materials M2O3 (M is Al, Ga, Fe, Cr, Sc or mixtures thereof), CuO and Ta2O5 are preferred. The mixed powder of starting materials is calcined at about 900xc2x0 C. for about 12 hours. The calcined powder is reground and pressed to 12.7 mm diameter/1-2 mm thick disks. The disks are sintered in air at about 950xc2x0 C. for 24 hours. In both the calcining and sintering steps, the temperature ramping up rate is about 200xc2x0 C./hour from room temperature, i.e., about 20xc2x0 C., to the calcining or sintering temperature and the cooling rate is about 150xc2x0 C./hour from the calcining or sintering temperature to room temperature, i.e., about 20xc2x0 C.
All of the Cu3Ta3MO12 phases of this invention crystallize in a cubic perovskite-related Im3 structure.
Dielectric measurements can be carried out on the disk samples. The faces of the disk-shaped samples are polished with a fine-grit sand or emery paper. Silver paint electrodes are applied on the faces and dried at 70-100xc2x0 C. The capacitance and the dielectric loss measurements can be performed by the two-terminal method using Hewlett-Packard 4275A and 4284A LCR bridges at a temperature of 25xc2x0 C. over a frequency range of from 1 kHz to 1 MHz. The capacitance, C, and the dissipation factor are read directly from the bridge. The dielectric constant (K) is calculated from the measured capacitance, C in picofarads, from the relationship, K=(100 C t)/(8.854 A), where t is thickness of the disk shaped sample in cm and A is the area of the electrode in cm2.